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package(n)			      Tcl Built-In Commands			       package(n)


       package - Facilities for package loading and version control

       package forget ?package package ...?
       package ifneeded package version ?script?
       package names
       package present ?-exact? package ?version?
       package provide package ?version?
       package require ?-exact? package ?version?
       package unknown ?command?
       package vcompare version1 version2
       package versions package
       package vsatisfies version1 version2

       This  command  keeps  a	simple	database of the packages available for use by the current
       interpreter and how to load them into the interpreter.  It supports multiple  versions  of
       each  package and arranges for the correct version of a package to be loaded based on what
       is needed by the application.  This command also  detects  and  reports	version  clashes.
       Typically, only the package require and package provide commands are invoked in normal Tcl
       scripts;  the other commands are used primarily by system scripts that maintain the  pack-
       age database.

       The  behavior  of  the package command is determined by its first argument.  The following
       forms are permitted:

       package forget ?package package ...?
	      Removes all information about each specified package from this interpreter, includ-
	      ing information provided by both package ifneeded and package provide.

       package ifneeded package version ?script?
	      This  command  typically appears only in system configuration scripts to set up the
	      package database.  It indicates that a particular version of a  particular  package
	      is  available  if  needed,  and that the package can be added to the interpreter by
	      executing script.  The script is saved in a database for use by subsequent  package
	      require  commands;   typically, script sets up auto-loading for the commands in the
	      package (or calls load and/or source directly), then  invokes  package  provide  to
	      indicate that the package is present.  There may be information in the database for
	      several different versions of a single package.  If the database	already  contains
	      information  for package and version, the new script replaces the existing one.  If
	      the script argument is omitted, the current script for version version  of  package
	      package  is  returned,  or  an empty string if no package ifneeded command has been
	      invoked for this package and version.

       package names
	      Returns a list of the names of all packages in the interpreter for which a  version
	      has  been  provided (via package provide) or for which a package ifneeded script is
	      available.  The order of elements in the list is arbitrary.

       package present ?-exact? package ?version?
	      This command is equivalent to package require except that it does not try and  load
	      the package if it is not already loaded.

       package provide package ?version?
	      This  command is invoked to indicate that version version of package package is now
	      present in the interpreter.  It is typically invoked once as part  of  an  ifneeded
	      script, and again by the package itself when it is finally loaded.  An error occurs
	      if a different version of package has been provided by a previous  package  provide
	      command.	 If the version argument is omitted, then the command returns the version
	      number that is currently provided, or an empty string if no package provide command
	      has been invoked for package in this interpreter.

       package require ?-exact? package ?version?
	      This  command is typically invoked by Tcl code that wishes to use a particular ver-
	      sion of a particular package.  The arguments indicate which package is wanted,  and
	      the  command  ensures  that  a  suitable	version of the package is loaded into the
	      interpreter.  If the command succeeds,  it  returns  the	version  number  that  is
	      loaded;	otherwise  it generates an error.  If both the -exact switch and the ver-
	      sion argument are specified then only the given version is acceptable.   If  -exact
	      is  omitted  but	version  is  specified, then versions later than version are also
	      acceptable as long as they have the same major version number as version.  If  both
	      -exact  and  version  are  omitted then any version whatsoever is acceptable.  If a
	      version of package has already been provided (by invoking the package provide  com-
	      mand),  then  its version number must satisfy the criteria given by -exact and ver-
	      sion and the command returns immediately.   Otherwise,  the  command  searches  the
	      database of information provided by previous package ifneeded commands to see if an
	      acceptable version of the package is available.  If so, the script for the  highest
	      acceptable version number is evaluated in the global namespace; it must do whatever
	      is necessary to load the package, including calling package provide for  the  pack-
	      age.   If  the  package ifneeded database does not contain an acceptable version of
	      the package and a package unknown command has been specified  for  the  interpreter
	      then  that  command  is  evaluated in the global namespace;  when it completes, Tcl
	      checks again to see if the package is  now  provided  or	if  there  is  a  package
	      ifneeded	script	for it.  If all of these steps fail to provide an acceptable ver-
	      sion of the package, then the command returns an error.

       package unknown ?command?
	      This command supplies a ``last resort'' command to invoke during package require if
	      no suitable version of a package can be found in the package ifneeded database.  If
	      the command argument is supplied, it contains the first part of  a  command;   when
	      the command is invoked during a package require command, Tcl appends two additional
	      arguments giving the desired package name and version.  For example, if command  is
	      foo  bar	and  later the command package require test 2.4 is invoked, then Tcl will
	      execute the command foo bar test 2.4 to load the package.  If no version number  is
	      supplied	to the package require command, then the version argument for the invoked
	      command will be an empty string.	If the package unknown command is invoked without
	      a  command  argument,  then  the	current package unknown script is returned, or an
	      empty string if there is none.  If command is specified as an  empty  string,  then
	      the current package unknown script is removed, if there is one.

       package vcompare version1 version2
	      Compares	the  two  version  numbers given by version1 and version2.  Returns -1 if
	      version1 is an earlier version than version2, 0 if they are equal, and  1  if  ver-
	      sion1 is later than version2.

       package versions package
	      Returns a list of all the version numbers of package for which information has been
	      provided by package ifneeded commands.

       package vsatisfies version1 version2
	      Returns 1 if scripts written for version2 will work unchanged with  version1  (i.e.
	      version1	is  equal  to  or greater than version2 and they both have the same major
	      version number), 0 otherwise.

       Version numbers consist of one or more decimal numbers separated by dots,  such	as  2  or
       1.162  or  The first number is called the major version number.  Larger numbers
       correspond to later versions of a package, with leftmost numbers having	greater  signifi-
       cance.	For example, version 2.1 is later than 1.3 and version 3.4.6 is later than 3.3.5.
       Missing fields are equivalent to zeroes:  version 1.3 is the same  as  version  1.3.0  and,  so it is earlier than 1.3.1 or  A later version number is assumed to be
       upwards compatible with an earlier version number as long as both versions have	the  same
       major  version  number.	 For  example,	Tcl  scripts written for version 2.3 of a package
       should work unchanged under versions 2.3.2, 2.4, and 2.5.1.  Changes in the major  version
       number  signify	incompatible changes: if code is written to use version 2.1 of a package,
       it is not guaranteed to work unmodified with either version 1.7.3 or version 3.1.

       The recommended way to use packages in Tcl is to invoke package require and  package  pro-
       vide commands in scripts, and use the procedure pkg_mkIndex to create package index files.
       Once you've done this, packages will  be  loaded  automatically	in  response  to  package
       require commands.  See the documentation for pkg_mkIndex for details.

       msgcat(n), packagens(n), pkgMkIndex(n)

       package, version

Tcl					       7.5				       package(n)
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